The present invention relates to a resilient protection and seal member for rolling bearings, arranged to be interposed between the outer and the inner race of the bearings in order to provide the seal between inner cavity of the said races and the outer ambient.
It is known that for many technical applications it is necessary to have at one's disposal rolling bearings having installed therein special protection members arranged to isolate the rolling bodies and the respective races from the surrounding ambient, so as to prevent the lubricant from coming out from the bearing and to avoid penetration of external contaminants, such as water or dust, into the bearing.
A first embodiment of such protection members consists of a shield formed by a metal lamination which is interposed between the outer and the inner race of the bearing. The lamination is shaped in such a way as to be connected by light fit with the bearing outer race on which a suitable seating is formed, and is provided with a central hole whose diameter is slightly larger than the outer diameter of the inner race of the bearing. In this way, between the edge of the hole formed on the lamination and the outer surface of the inner race there is created a pre-established clearance which forms a labyrinth seal. When desiring to ensure the seal on both sides of the bearing, two laminations of the type described are used disposing one of them on each side. In this case the bearing is called a completely shielded bearing.
A second embodiment of said protection members consists in a sealing assembly comprising a metal ring of suitable shape such as to be connected by light fit with a special seating formed on the outer race of the rolling bearing and a resilient annular lip, made of an elastomeric material, connected in any suitable manner with the said ring and arranged to provide a sliding seal with a special surface formed on the inner race of the bearing. A protection on both sides of the said bearing is obtained by using two seal assemblies of the type described hereinabove, one on each side. In this case the bearing is called a completely sealed bearing.
The embodiments described hereinabove have numerous disadvantages, as regards both the installation and the operation.
In particular, the assembly system by shrinking between the seating formed on the outer race of the bearing and the lamination or the metal ring gives rise to a deformation of these latter and renders impossible an eventual disassembly of the protection member. This renders difficult or impossible both the substitution of the lubricant within the bearing after a certain time of operation and the periodical maintenance. In fact, in case of using a metal shield it is, of course, impossible to introduce a new lubricant without breaking the shield, whilst in case of using the sealing assembly described hereinabove it is possible to perforate the annular lip by means of a needle and add lubricant by means of a syringe; this method however is inconvenient and allows adding only small quantities of lubricant. Thus, the completely shielded bearings or the completely sealed bearings have to be designed for a duration of operation equal to that of the reserve of lubricant contained therein, and since this reserve is limited and not renewable, these bearings have short durations.
The shielded bearings have another serious disadvantage. For the sealing action to be efficient, the clearance between the edge of the hole of the metal lamination and the outer surface of the inner race must be as small as possible. However, if it is very small, because of the working tolerances an interference may take place between the lamination and the inner race if the maximum diameter of this latter (rated diameter of the race plus maximum error above the tolerance) results in being larger than the minimum diameter of the hole of the lamination (rated diameter of the hole less maximum error below the tolerance). In case of interference, since the lamination is made of a metal material, a sliding with the inner race of the bearing takes place, with consequent serious damages and loss of efficiency not only of the seal, but also of the bearing. To ensure avoiding this possibility of interference, one may choose larger clearances. However, in this case, when the hole has a diameter larger than the rated diameter and the race has an outer diameter smaller than the rated diameter (which is a case opposed to the former), the clearance results in being so large as to considerably reduce or even completely eliminate the sealing action.
The sealed bearings, instead, if they have efficient seals, they are subject to high kinematic losses because of the friction between the sliding lip and the inner race. In bearings intended to be used in applications requiring a very low friction, these losses result in being inacceptable.